I still use VST rack instrument because I can have multiple midi parts assigned to the same instrument very frequently. However in cases where I want to create another exact duplicate of a VST instrument it cannot be done. Also if I have a great VST rack setup I can't easily save the entire rack to use on another song. I use Vienna Ensemble on a slave machine and it allows you to do both of these things with complex setups and its a real timesaver at times. So..

Ability to duplicate VSTis
Ability to preserve entire Rack in one operation with the ability to load everything from that rack onto another song with one operation. This would ideally work on load by bringing up the list of instruments in that VST rack being loaded allows you to select them to load or not in a similar way to how load track archive works.

- A Midi/Return type of track which carries both the audio one of the output of the rack and a midi input (I think Logic does something like that).

It is such a pain to have to change anything in the Rack and LOSE ALL YOUR configurations in the outputs, as they disappear... I happens when you change a vst2 plugin to a vst3 one, or Kontakt 5 to Kontakt 6.

Another option would be make Instrument tracks really useful for multitimbral purposes and VEPro, and also MIDI SEND.